In Vivo Fast Induction of Homogeneous Autopolyploids via Callus in Sour Jujube (Ziziphus acidojujuba Cheng et Liu)

Polyploidization has been demonstrated as a very effective approach in fruit tree improvement. Sour jujube (Ziziphus acidojujuba Cheng et Liu) is a promising diploid wild, traditional fruit species (2n = 2x = 24) that is rich in vitamin C, which is the main rootstock of Chinese jujube (Z. jujuba Mill.). The novel method we developed for rapid in vivo induction of homogeneous autopolyploids (IVIHA) via callus in Chinese jujube was first applied and further optimized in sour jujube. Under optimized conditions, an average of one pure autotetraploid shoot could be regenerated from one treated branch, thereby indicating a relatively high efficiency rate. A total of 9 pure autotetraploid genotypes were created, and one of these was released as a new cultivar named ‘Zhuguang’ in 2015. Moreover, unexpected octoploids and hexaploids were also simultaneously created and detected. The leaves of tetraploids were thicker, broader, and darker in color than those of the original diploids, whereas the leaf sizes of octoploids were much smaller compared to that of diploids. However, stoma size increased with the occurrence of ploidy, mainly from diploid to octoploid. The well grown ploidies of jujube included diploids, triploids, and tetraploids. Anatomical observation indicated that adventitious buds/shoots emerged from the callus that formed on the cut, which was then followed by the development of connective vascular tissues between the adventitious bud and the stock plant tissue. This study demonstrates the universality of the IVIHA method that was initially developed in Chinese jujube, as well as provides a foundation for high-efficiency pure polyploid induction in sour jujube.